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Re: Rain Sheets, why?



Brad,

I think there is at least some truth in what I am about to say.

In clouds as drops are forming, the drops ( I think it is
actually ice balls ( hail) at this point) are held aloft by updrafts.
That is the terminal velocity of the drop is less than the upward
velocity of the wind. Wind in thunderstorms is very gusty. A sheet of
rain occurs after a vertical gust has ended ( by moving on or pressures
equalizing or whatever) and the drops falling to the ground.

Usually the longer a drop is held aloft the larger it grows with
helps explain why there are large drops is the sheets.

Thanks
roger haar
U of AZ


****************************************************************
On Tue, 27 May 1997, Brad Shue wrote:

Here in Arkansas, we had some pretty nasty rain tonight. A few grad
students and myself were sitting around watching the lightning and the
rain after a cookout. Why does the rain come down in sheets came up.

The best we could come up with was that the larger rain droplets reach
terminal velocity and cause a wave-like disturbance in the wind from the
storm and other droplets get caught in this initial phase. Much like the
Bernouli demonstration, the smaller droplets get pulled into the area
behind the larger drops because of the reduced pressure.

This effect causes waves of rain to form with the larger drops leading the
way. From what I have experienced, the big drops are the "leaders" of
each wave.

Any thoughts on this? It is a nice summer topic most of us can relate to.
================================================================
James Bradford Shue jshue@comp.uark.edu
University of Arkansas Voice phone:(501) 575-6059
Physics Lab/Demo Curator FAX Number: (501) 575-4580
WWW Page http://comp.uark.edu/~jshue